1. Field of the Invention
The present invention generally relates to test devices for rapid assays and more specifically to device and method for a novel lateral-flow assay.
2. Discussion of the Related Art
Rapid diagnostic in vitro assays for detecting the presence of biological compounds have become routine for a variety of applications including medical diagnosis, environmental monitoring, forensic toxicology and food pathogen testing. The ever-increasing demand for new, low-cost and sensitive rapid assays have generated many new developments in this field over recent years. However there is still a continuous need for new and improved detection methods and devices of higher sensitivity and of lower cost. In particular, there is a great demand for low-cost point-of-care clinical diagnostics kits that can be used by untrained persons.
One popular format for performing one-step rapid assays is the lateral flow assay technology where a sample is applied at one end of a test strip pre-treated with assay specific reagents. The sample is drawn along the strip by capillary action, traveling through an indicator zone where the appearance of a visible, or otherwise detectable signal, indicates the presence of the analyte in the sample. The indicator zone typically comprises a member of a specific binding pair immobilized to the strip in a defined area, typically a line. The strip may further comprise a labeling zone, located downstream the sample application zone, provided with a labeling substance. The lateral flow assay is carried out by applying the sample suspected of containing the analyte at the sample receiving end and allowing it to travel along the strip by capillary action, to pick up the label compound when present, and further downstream to be captured and concentrated at the detection/capture zone. There exist many variations of this basic structure, regarding the number and nature of the immobilized, labeling and other substances located along the strip and their interaction with the analyte, as well as to the nature and formation of the detectable signal. For example, the detectable signal does not necessarily result from a direct interaction between the immobilized substance and the analyte but, depending on the specific assay and strip structure, may result from indirect interaction with a secondary product that is formed upstream of the immobilized substance and whose production requires the presence of the analyte. In accordance with other variations, the immobilized reagent may serve to capture un-reacted upstream reagents, for example unbound label reagent, while the detection zone is located downstream the capture zone. However, in most cases, prior art lateral flow strips include at least one pre-immobilized reagent.
The present invention provides a novel strip for lateral flow assays where all the detection reactants are movably bound to the strip and wherein the capture zone is formed at the interface between two sequentially ordered flow matrices of different characteristics.
In particular, the strip of the present invention is suitable for, but is not limited to, the detection of enzymes, or enzymes substrates, in bodily fluids.